Water-blocking in optical-fiber buffer tubes and fiber optic cables typically has been accomplished by using petroleum-based filling gels (e.g., grease). By completely filling all of the free space inside a buffer tube that contains an optical fiber or optical-fiber bundle, the filling gel blocks the ingress of water into the fiber optic cable.
Moreover, being a thixotropic material, the filling gel also tends to mechanically couple the optical fiber(s) to the buffer tube. Such mechanical coupling prevents the optical fiber(s) from retracting inside the buffer tube as the buffer tube is processed during manufacturing, as the cable is installed or otherwise handled in the field, or as the cable is subjected to thermally induced dimensional changes from environmental exposure.
Although relatively effective for controlling cable flooding, the petroleum-based filling gels are inconvenient during cable repair and optical-fiber splicing. The use of such gels requires cleaning the petroleum-based material from optical fibers prior to splicing (and sometimes from equipment and personnel, too), which can be messy and time consuming. Consequently, using conventional filling greases is often undesirable.
Various dry-cable designs have been developed to eliminate filling greases while providing some water-blocking and coupling functions. In either loose tube fiber cables or ribbon cables, a totally dry design eliminates the filling gel from the enclosed buffer tubes. In a totally dry cable, for example, filling gel may be replaced by a water-blocking element, such as a tape or a yarn carrying a water-swellable material (e.g., water-swellable powder). Water-swellable powders are dry to the touch and, when bound to a carrier tape or yarn, can be readily removed during field operations (e.g., splicing).
Optical fibers are sensitive to mechanical loads, which can cause undesirable microbending. Those having ordinary skill in the art know that microbending is induced when small stresses are applied along the length of an optical fiber, perturbing the optical path through microscopically small deflections in the core.
Water-swellable powders consist of finely ground hard particles. The size and hardness of such particulates may be sufficient to cause microbending and optical attenuation in the optical fibers they contact.
Accordingly, there is a need for a more effective solution to dry cable design. In particular, there is a need for a grease-free water-blocking element that reduces microbending losses in optical fibers yet effectively blocks the longitudinal movement of water inside a fiber optic cable and its constituent buffer tubes.